1. Field of the Invention
The present invention relates to a dimension measuring apparatus, a dimension measuring method and a program for dimension measuring apparatus, and more specifically relates to improvement in dimension measuring apparatus which photographs a workpiece on a stage with different photographing magnifications to measure a dimension of the workpiece.
2. Description of Related Art
In general, a dimension measuring apparatus is an apparatus for measuring a dimension of a workpiece based on an edge of a workpiece image obtained by photographing a workpiece, and may be called an image measuring apparatus (e.g., Unexamined Japanese Patent Publication No. 2009-300124, Unexamined Japanese Patent Publication No. 2009-300125, Unexamined Japanese Patent Publication No. 2010-19667). Normally, a workpiece is placed in a movable stage that is movable in X-axis, Y-axis and Z-axis directions. The movable stage is moved in the Z-axis direction to perform focus adjustment of the workpiece image, and moved in the X-axis and Y-axis directions to perform positioning of the workpiece within a field of view.
The workpiece image has an extremely accurate similar shape to that of the workpiece regardless of the position of the movable stage in the Z-axis direction, and hence determining a distance and an angle on the image can detect an actual dimension on the workpiece image. In the case of measuring the dimension of the workpiece by means of such a dimension measuring apparatus, increasing a photographing magnification can lead to improvement in measurement accuracy. However, there has been a problem in that increasing the photographing magnification narrows the field of view to reduce a photographed area on the stage, thereby making the workpiece difficult to place within the photographed area. It is therefore considered that high-magnification photographing and low-magnification photographing are made switchable so as to perform postural adjustment of the workpiece and positioning thereof into a high-magnification field of view, while viewing a screen display of the workpiece image obtained by low-magnification photographing. However, there has been a problem with the conventional dimension measuring apparatus in that switching of the photographing magnification and postural adjustment and positioning of the workpiece should be manually performed, to cause an operating procedure to be complicated and dimension measurement to take a long time.